In the aviation industry safety rules require that aircraft components are constantly monitored for fatigue as these components are subjected to a large number of significant and prolonged mechanical stresses (or loads). Accordingly, these components are subjected to overhauls on a regular and recurrent basis. A number of specific components, such as landing gears, engine pylons, etc. can conceivably benefit from a sensor configuration capable of recording maximum loads and therefore providing valuable information on effects of hard landing and other overloading conditions which are difficult to deduct from presently known flight recording apparatuses.
In civil structures such as buildings, bridges, overpasses, dams, oil reservoirs, pressure vessels and towers knowing the history of strain experienced by the structures can present valuable information for assisting in predicting the maximum stochastic loads and the remaining working life of the structure as well as assisting in assessing the integrity of the structure.
Such information could also assist civil engineers conducting investigations related to determining the necessity of structural reinforcements in order to address the effects of climatic changes (i.e.: both static and dynamic loads in the form of wind, snow, water levels, among other loads that will be readily appreciated by the skilled person), urban changes (such as increasing the magnitude of transport loads on a bridge or roadway) and technological process changes (which can lead to increased loads due to overhead cranes, conveyors, etc.) on industrial buildings and other pieces of civil infrastructure.
When structures are tested in a laboratory environment in order to monitor strain or displacement there are a number of limitations (including space limitations and/or limitations to the number of available data logging channels) that could be overcome by using simple and inexpensive self-contained recording gauges.
For an overall review of prior art solutions for micro-electromechanical systems in a variety of industrial and commercial applications, the reader is directed to the following academic and patent publications:    G. Krijnen and N. Tas, “Micromechanical Actuators”, MESA+ Research Institute, Transducer Technology Laboratory, University of Twente, Enschede, The Netherlands    A. S. Holmes, S. Lucyszyn, S. Pranonsatit and G. Hong, “Rotary RF MEMS Switch based on the Wobble Motor Principle”, Optical and Semiconductor Devices Group, Department of Electronic & Electronic Engineering, Imperial College London, London, UK    Z. Li and N. Tien, “Low-Cost Electroplated Vertical Comb-Drive”, Berkeley Sensor and Actuator Center, Department of Electrical and Computer Engineering, University of California, Davis, Calif.    D. M. Tanner, J. A. Walraven, K. Helgesen, L. W. Irwin, F. Brown, N. F. Smith, and N. Masters, “MEMS reliability in shock environments”, Sandia National Laboratories, Albuquerque, N. Mex., Presented at IEEE International Reliability Physics Symposium in San Jose, Calif., Apr. 10-13, 2000, pp. 129-138    U.S. Patent Publication No. 2012/0035864 to Frydenhal—Determining an Equivalent Mechanical Load    U.S. Pat. No. 8,600,611 to Seize—System and Method for Measuring Fatigue for Mechanical Components of an Aircraft and Aircraft Maintenance Method    Multiple Authors, “Aging Aircraft Fleets: Structural and Other Subsystem Aspects”, North Atlantic Treaty Organization, Research and Technology Organization, Neuilly-Sur-Seine Cedex, France, presented 13-16 Nov. 2000 in Sofia, Bulgaria    U.S. Pat. No. 7,148,579 to Pinkerton et al.—Energy Conversion Systems Utilizing Parallel Array of Automatic Switches and Generators    S. Willis, “Next Generation Data Acquisition Technologies for Aging Aircraft”, ACRA CONTROL, Dublin, Ireland, 7th DSTO International Conference on Health & Usage Monitoring    A. C. J. Glover, “Non-Destructive Testing Techniques for Aerospace Applications”, Inspection and Maintenance Systems Division, Olympus Australia Pty Ltd, Victoria, Australia    U.S. Pat. No. 7,928,343 to King et al—Microcantilever Heater-Thermometer with Integrated Temperature-Compensated Strain Sensor    U.S. Pat. No. 7,839,028 to Pinkerton et al.—Nanoelectromechanical Systems and Methods for Making the Same    U.S. Pat. No. 6,744,338 to Nikitin—Resonant Operation of MEMS Switch    U.S. Pat. No. 5,910,837 to Gimzewski—Photomechanical Transducer    U.S. Pat. No. 5,739,425 to Binnig et al.—Cantilever with Integrated Deflection Sensor    U.S. Patent Publication No. 2010/0176898 to Kihara—MEMS Device and Method for Manufacturing the Same    U.S. Patent Publication No. 2004/0228258 to Binnig et al.—Method and Apparatus for Reading and Array of Thermal    European Patent No. 1,226,437 to Bailer et al.—Cantilever Sensors and Transducers    T. L. Haglage, “Flight Test Evaluation of a Scratch Strain Gage”, Air Force Flight Dynamics Laboratory (FDTR), Wright-Patterson Air Force Base, Ohio    U.S. Patent Publication No. 2007/0062299 to Mian et al.—MEMS-based Monitoring    U.S. Pat. No. 5,780,727 to Gimzewski—Electromechanical Transducer    U.S. Pat. No. 5,936,411 to Jacobsen et al.—Apparatus and Method for Measuring Strain within a Structure    U.S. Pat. No. 6,492,820 to Adachi et al.—Displacement Measuring Device    U.S. Pat. No. 7,412,899 to Mian et al.—MEMS-based Monitoring    U.S. Pat. No. 7,832,281 to Mian et al.—MEMS-based Monitoring    U.S. Pat. No. 6,480,792 to Prenderast—Fatigue Monitoring Systems and Methods Incorporating Neural Networks    D. M. Vidrine, “A Sequential Strain Monitor and Recorder for Use in Aircraft Fatigue Life Prediction”, Naval Postgraduate School, Monterey, Calif.    K. L. Singh and D. V. Venkatasubramanyam, “Techniques to Generate and Optimize the Load Spectra for an Aircraft”, Structural Technologies Division, National Aerospace Laboratories, Bengaluru, India, 3rd International Conference on Integrity, Reliability and Failure, Porto/Portugal, 20-24 Jul. 2009    L. Molent and B. Aktepe, “Review of fatigue monitoring of agile military aircraft”, Aeronautical and Maritime Research Laboratory, Defence Science and Technology Organisation, Victoria, Australia    S. Ariduru, “Fatigue Life Calculation by Rainflow Cycle Counting Method”, The Graduate School of Natural and Applied Sciences of Middle East Technical University    C. Martin, “A Review of Australian and New Zealand Investigations on Aeronautical Fatigue During the Period Between April 1995 to March 1997”, Airframes and Engines Division, Aeronautical and Maritime Research Laboratory, Defence Science and Technology Organisation, Victoria, Australia    L. Molent, “Proposed Specifications for an Unified Strain and Flight Parameter Based Aircraft Fatigue Usage Monitoring System”, Airframes and Engines Division, Aeronautical and Maritime Research Laboratory, Defence Science and Technology Organisation, Victoria, Australia    D. E. Gordon, S. B. Kirschner and S. D. Manning, “Development of Fatigue and Crack Propagation Design & Analysis Methodology in a Corrosive Environment for Typical Mechanically-Fastened Joints”, General Dynamics Corporation for Naval Development Center, Department of the Navy    U.S. Pat. No. 7,680,630 to Schmidt—Monitoring A Parameter with Low Power Consumption for Aircraft Landing Gear-Data Logger    U.S. Patent Publication No. 2009/0319102 to Winterhalter et al.—Flight Recorder Having Integral Reserve Power Supply Within Form Factor of Enclosure and Method Therefor    S. W. Arms, C. P. Townsend, D. L Churchill, S. M. Moon and N. Phan, “Energy Harvesting Wireless Sensors for Helicopter Damage Tracking”, American Helicopter Society International Inc., proceedings of AHS International Forum 62, HUMS III session, Phoenix, Ariz., May 11, 2006    K. Matsumoto, K. Saruwatari and Y. Suzuki, “Vibration-Powered Battery-less Sensor Node Using MEMS Electret Generator”, Department of Mechanical Engineering, The University of Tokyo, Tokyo, Japan, TechnoDesign Co., Ltd, Kumamoto, Japan    DSTO International Conference on Health and Usage Monitoring, Aeronautical and Maritime Research Laboratory, Defence Science and Technology Organisation, Victoria, Australia, presented in Melbourne, Feb. 19-20, 2001    J. H. Galbreath, C. P. Townsend, S. W. Mundell, M. J. Hamel, B. Esser, D. Huston, S. W. Arms, “Civil Structure Strain Monitoring with Power-Efficient, High-Speed Wireless Sensor Networks”, MicroStrain, Inc., Williston, Vt., University of Vermont, Dept. Of Civil & Mechanical Engineering, Burlington, Vt., USA, Presented at 4th Int'l Workshop on Structural Health Monitoring Stanford University, Stanford Calif., Sep. 15-17, 2003    S. W. Arms, C. P. Townsend, J. H. Galbreath, S. J. DiStasi, D. Liebschutz, and N. Phan, “Flight Testing of Wireless Sensing Networks for Rotorcraft Structural Health and Usage Management Systems”, MicroStrain, Inc., Williston, Vt., USA, Navy/NAVAIR, Structures Division, Patuxent River, Md., 7th DSTO International Conference on Health & Usage Monitoring    D. A. Howell and H. W. Shenton III, “System for In-Service Strain Monitoring of Ordinary Bridges”, JOURNAL OF BRIDGE ENGINEERING© ASCE, November/December 2006    K. A. Jason and K. Surya, “A Survey of Health and Usage Monitoring System in Contemporary Aircraft”, International Journal of Engineering and Technical Research (IJETR), ISSN: 2321-0869, Volume-1, Issue-9, November 2013    M. Neumair and W. Luber, “Structural Health Monitoring For Military Aircraft Considering Vibration”, EADS Deutschland GmbH, Munich, Germany    H. Murayama, D. Wada, and H. Igawa, “Structural Health Monitoring by Using Fiber-Optic Distributed Strain Sensors With High Spatial Resolution”, School of Engineering, The University of Tokyo, Tokyo, Japan, Japan Aerospace Exploration Agency, 6-13-1 Ohsawa, Mitaka, Tokyo, 181-0015 Japan, Photonic Sensors (2013) Vol. 3, No. 4: 355-376    S. Maley J. Plets and N. D. Phan, “US Navy Roadmap to Structural Health and Usage Monitoring—The Present and Future”, Structures Division, Naval Air Systems Command, Patuxent River, Md., American Helicopter Society International, Inc., presented at the American Helicopter Society 63rd Annual Forum, Virginia Beach, Va., May 1-3, 2007    U.S. Pat. No. 5,421,204 to Svaty, Jr.—Structural Monitoring System    U.S. Pat. No. 8,618,928 to Weed et al.—System and Methods for Wireless Health Monitoring of a Locator Beacon which Aids the Detection and Location of a Vehicle and/or People    U.S. Patent Publication No. U.S. 2013/0278377 to Slupsky et al.—Wireless Sensor Device    S. Mahlknecht, J. Glaser and T. Herndl, “PAWIS: Towards a Power Aware System Architecture for a SOC/SIP Wireless Sensor and Actor Node Implementation”, Institute of Computer Technology, Vienna University of Technology, Vienna, Austria, Infineon Technologies Austria AG, Vienna, Austria
In aerospace applications, the components used to attach the propulsion system (i.e.: the turbo-jet engines) to the airplane as well as components such as wings, landing gears and critical parts of the fuselage are subjected to strict systematic inspections. Each overhaul requires removing the airplane from service in order to access or remove critical parts in order to carry out these tests.
To address these issues, Health and Usage Monitoring Systems (HUMS) have been developed that utilize data collection and analysis techniques to help ensure availability, reliability and safety of vehicles, specifically commercial vehicles such as aircraft and trains.
The importance and benefits of structural health monitoring are well-known and clearly evident and include significant risk reduction, particularly in instances of severe usage of an aircraft, and the potential prolongation of the life of an aircraft when the measured usage spectrum is in fact less intense than the designed usage spectrum. Particularly, HUMS can significantly reduce scheduled maintenance, aborted missions and maintenance test flights in both fixed and rotary aircraft applications (i.e.: airplanes and helicopters).
Historically, fatigue prediction methodologies were an important part of an aircraft's safety and maintenance programs. For example, U.S. Pat. No. 8,600,611 to Seize teaches that the frequency of the overhauls is determined in advance and an overhaul is carried out on expiration of each preset time period (for example every 2600 flight cycles: takeoff-flight-landing), irrespective of the real state of fatigue of the component. Seize contemplates avoiding any risk that can arise when an overhaul is undertaken too long after a fatigue state develops and an intervention, such as a repair or a replacement of the component, is required. Seize also provides that this relevant time period must be selected (either through computation or empirical analysis) based on the minimum period beyond which there is a risk that the component will fail, even if this risk remains statistically marginal.
This selected minimum period therefore corresponds to situations where the specific components are subjected to accidental, over-the-limit stresses; accordingly, many overhauls are carried out on components that could have been used without danger for longer since they have not been subjected to accidental stresses. Finally, in the absence of analysis of the real stresses to which a component has been subjected, the worst case scenario is always taken with respect to the possible damage that has occurred to the component, which can lead to overhauls that are often conducted prematurely.
Moreover, frequent overhauls can also introduce the additional possibility that an error may occur during re-assembly of the overhauled component during re-installation.
In some instances, data is collected by the inertial forces sensing unit of the airplane to determine whether the airplane has been subjected to exceptional stresses (such as a hard landing), however it can be difficult and costly to deduct an accurate and representative picture of the overloading of a variety of the components due to the sheer complexity of the overall mechanical system and the variance of the loading conditions, thereby resulting in a less accurate fatigue prediction.
Therefore, there is a need for a portable and self contained sensory means capable of recording and storing information relating to the peak stresses experienced by a particular component and the distribution of the stress levels historically occurring in the structure without adding much weight or complexity to the structure in terms of service and or reducing the reliability of data acquisition system or aircraft itself.
The aforementioned U.S. Pat. No. 8,600,611 to Seize provides a solution for employing multiple sensors that each have pre-set threshold levels for providing data collection and analysis. Disadvantages presented by this approach relate to the use of multiple sensors, which can be difficult to mount at close proximity to the point of interest thereby introducing error in stress estimation, which can be substantial. In addition, the use of separate sensors (each pre-set for a specific threshold level) complicates the device and can lead to increased power consumption.
SU983,441 to the present inventor P. Okulov teaches a multi-contact discrete displacement sensor which provides for automatic discrimination of threshold levels dividing the overall displacement into a number of levels predetermined by the gaps between contacting plates. This sensor employs a stack of electrically conductive flexible membranes as an array of contact plates.
Another known variant of a multi-contact discrete displacement sensor that uses an electro-conductive flexible cantilever plates is described in association with a system for data acquisition from the crane loads as discussed in PhD dissertation “Analysis of join effects of loads from suspended cranes and snow on metal structures of roofs of industrial buildings”, Moscow, 1985, MISI (Moscow State University of Civil Engineering formerly known as MISI) by the present inventor, P. Okulov.
Therefore, in one embodiment it is contemplated that the present invention can provide a device that can be easily attachable and detachable to the underlying support structure, is operable in an autonomous mode and can store information without the need for any external device for an extended period with the possibility of easy retrieval of said data through wireless means or a simple interface.